Binder composition for all-solid-state secondary battery, slurry composition for all-solid-state secondary battery, solid electrolyte-containing layer, and all-solid-state secondary battery

ABSTRACT

Provided is a binder composition for an all-solid-state secondary battery with which it is possible to form a solid electrolyte-containing layer that can cause an all-solid-state secondary battery to display excellent high-temperature cycle characteristics. The binder composition for an all-solid-state secondary battery contains an acrylic polymer and not less than 500 mass ppm and not more than 20,000 mass ppm of a phosphoric acid ester emulsifier relative to the acrylic polymer.

TECHNICAL FIELD

The present disclosure relates to a binder composition for anall-solid-state secondary battery, a slurry composition for anall-solid-state secondary battery, a solid electrolyte-containing layer,and an all-solid-state secondary battery.

BACKGROUND

Demand for secondary batteries such as lithium ion secondary batterieshas been increasing in recent years for various applications such asmobile information terminals, mobile electronic devices, and othermobile terminals, and also domestic small power storage devices,motorcycles, electric vehicles, and hybrid electric vehicles. Thewidespread use of secondary batteries in such applications has beenaccompanied by demand for further improvement of secondary batterysafety.

For this reason, all-solid-state secondary batteries in which a solidelectrolyte is used instead of an organic solvent electrolyte havinghigh flammability and high danger of ignition upon leakage areattracting attention as secondary batteries having high safety.

An all-solid-state secondary battery includes a positive electrode, anegative electrode, and a solid electrolyte layer located between thepositive electrode and the negative electrode. An electrode (positiveelectrode or negative electrode) of an all-solid-state secondary batteryis formed by, for example, applying a slurry composition that containsan electrode active material (positive electrode active material ornegative electrode active material), a binder, and a solid electrolyteonto a current collector, and then drying the slurry composition thathas been applied to provide an electrode mixed material layer (positiveelectrode mixed material layer or negative electrode mixed materiallayer) on the current collector. Moreover, a solid electrolyte layer ofan all-solid-state secondary battery is formed by, for example, applyinga slurry composition that contains a binder and a solid electrolyte ontoan electrode or a releasable substrate, and then drying the slurrycomposition that has been applied.

Acrylic polymers are conventionally used as binders in the formation ofsolid electrolyte layers. For example, in Patent Literature (PTL) 1,monomers are emulsion polymerized in water in the presence of sodiumdodecylbenzenesulfonate as an emulsifier to obtain a water dispersion ofan acrylic polymer, and then solvent exchange with an organic solvent isperformed to produce a binder composition that contains the acrylicpolymer and the organic solvent.

CITATION LIST Patent Literature

PTL 1: WO2016/152262A1

SUMMARY Technical Problem

Particularly in recent years, enhancing cycle characteristics ofall-solid-state secondary batteries under high-temperature conditions(hereinafter, referred to as “high-temperature cycle characteristics”)has been an issue due to all-solid-state secondary batteries often beingexposed to high-temperature conditions (for example, 80° C. or higher)in fields such as electric vehicles, for example. In other words, thereis demand for forming a layer that contains a solid electrolyte(hereinafter, referred to as a “solid electrolyte-containing layer”)such as a solid electrolyte layer or an electrode mixed material layerand ensuring adequate high-temperature cycle characteristics of anall-solid-state secondary battery using a binder composition thatcontains an acrylic polymer.

Accordingly, one object of the present disclosure is to provide a bindercomposition for an all-solid-state secondary battery and a slurrycomposition for an all-solid-state secondary battery with which it ispossible to form a solid electrolyte-containing layer that can cause anall-solid-state secondary battery to display excellent high-temperaturecycle characteristics.

Another object of the present disclosure is to provide a solidelectrolyte-containing layer that can cause an all-solid-state secondarybattery to display excellent high-temperature cycle characteristics andan all-solid-state secondary battery that has excellent high-temperaturecycle characteristics.

Solution to Problem

The inventors conducted diligent investigation with the aim of solvingthe problem set forth above. The inventors reached a new discovery thata solid electrolyte-containing layer that can cause an all-solid-statesecondary battery to display excellent high-temperature cyclecharacteristics can be formed by using a slurry composition that isproduced using a binder composition containing an acrylic polymer and aspecific amount of a phosphoric acid ester emulsifier, and, in thismanner, the inventors completed the present disclosure.

Specifically, the present disclosure aims to advantageously solve theproblem set forth above, and a presently disclosed binder compositionfor an all-solid-state secondary battery comprises: an acrylic polymer;and not less than 500 mass ppm and not more than 20,000 mass ppm of aphosphoric acid ester emulsifier relative to the acrylic polymer. Byforming a solid electrolyte-containing layer using a slurry compositioncontaining a binder composition that contains an acrylic polymer and aphosphoric acid ester emulsifier and in which the amount of thephosphoric acid ester emulsifier relative to the acrylic polymer is aproportion that is within the range set forth above in this manner, itis possible to cause an all-solid-state secondary battery to displayexcellent high-temperature cycle characteristics.

Note that the term “acrylic polymer” as used in the present disclosuremeans a polymer that includes a (meth)acrylic acid ester monomer unit ina proportion of 50 mass % or more.

Also note that in the present disclosure, “(meth)acryl” is used toindicate “acryl” and/or “methacryl”.

Moreover, the phrase “includes a monomer unit” as used in the presentdisclosure means that “a polymer obtained using the monomer includes arepeating unit derived from the monomer”.

Furthermore, the proportion in which each repeating unit (monomer unit)of a polymer is included in the polymer can be measured by a nuclearmagnetic resonance (NMR) method such as ¹H-NMR or ¹³C-NMR.

Note that the content of a “phosphoric acid ester emulsifier” relativeto an “acrylic polymer” referred to in the present disclosure can bedetermined by gel permeation chromatography (GPC).

In the presently disclosed binder composition for an all-solid-statesecondary battery, the acrylic polymer preferably includes both an ethylacrylate unit and an n-butyl acrylate unit. When a polymer that includesboth an ethyl acrylate unit and an n-butyl acrylate unit is used as theacrylic polymer, high-temperature cycle characteristics of anall-solid-state secondary battery can be sufficiently improved.

In the presently disclosed binder composition for an all-solid-statesecondary battery, an emulsion polymer can be used as the acrylicpolymer.

Also, the presently disclosed binder composition for an all-solid-statesecondary battery can further comprise an organic solvent.

Moreover, the present disclosure aims to advantageously solve theproblem set forth above, and a presently disclosed slurry compositionfor an all-solid-state secondary battery comprises: a solid electrolyte;and the above-described binder composition for an all-solid-statesecondary battery that contains an organic solvent. By forming a solidelectrolyte-containing layer using a slurry composition that contains asolid electrolyte and the binder composition containing an organicsolvent in this manner, it is possible to cause an all-solid-statesecondary battery to display excellent high-temperature cyclecharacteristics.

The presently disclosed slurry composition for an all-solid-statesecondary battery can contain an inorganic solid electrolyte as thesolid electrolyte.

Also, the presently disclosed slurry composition for an all-solid-statesecondary battery can further comprise an electrode active material. Anelectrode mixed material layer that can cause an all-solid-statesecondary battery to display excellent high-temperature cyclecharacteristics can be well formed by using the slurry composition foran all-solid-state secondary battery that contains an electrode activematerial.

Furthermore, the present disclosure aims to advantageously solve theproblem set forth above, and a presently disclosed solidelectrolyte-containing layer is formed using any one of the slurrycompositions for an all-solid-state secondary battery set forth above.The solid electrolyte-containing layer formed using the slurrycomposition for an all-solid-state secondary battery set forth above cancause an all-solid-state secondary battery to display excellenthigh-temperature cycle characteristics.

Also, the present disclosure aims to advantageously solve the problemset forth above, and a presently disclosed all-solid-state secondarybattery comprises the solid electrolyte-containing layer set forthabove. An all-solid-state secondary battery that can display excellenthigh-temperature cycle characteristics is obtained by using the solidelectrolyte-containing layer set forth above.

Advantageous Effect

According to the present disclosure, it is possible to provide a bindercomposition for an all-solid-state secondary battery and a slurrycomposition for an all-solid-state secondary battery with which it ispossible to form a solid electrolyte-containing layer that can cause anall-solid-state secondary battery to display excellent high-temperaturecycle characteristics.

Moreover, according to the present disclosure, it is possible to providea solid electrolyte-containing layer that can cause an all-solid-statesecondary battery to display excellent high-temperature cyclecharacteristics and an all-solid-state secondary battery that hasexcellent high-temperature cycle characteristics.

DETAILED DESCRIPTION

The following provides a detailed description of embodiments of thepresent disclosure.

The presently disclosed binder composition for an all-solid-statesecondary battery is used in production of the presently disclosedslurry composition for an all-solid-state secondary battery. Moreover,the presently disclosed slurry composition for an all-solid-statesecondary battery is used in formation of a solid electrolyte-containinglayer, such as an electrode mixed material layer or a solid electrolytelayer, that is used in an all-solid-state secondary battery, such as anall-solid-state lithium ion secondary battery. Furthermore, thepresently disclosed all-solid-state secondary battery is anall-solid-state secondary battery in which at least one layer selectedfrom the group consisting of a positive electrode mixed material layerof a positive electrode, a negative electrode mixed material layer of anegative electrode, and a solid electrolyte layer is the presentlydisclosed solid electrolyte-containing layer formed using the presentlydisclosed slurry composition for an all-solid-state secondary battery.

(Binder Composition for all-Solid-State Secondary Battery)

The presently disclosed binder composition contains an acrylic polymerand a phosphoric acid ester emulsifier, and can optionally furthercontain other components such as an organic solvent. The content of thephosphoric acid ester emulsifier in the presently disclosed bindercomposition is required to be not less than 500 mass ppm and not morethan 20,000 mass ppm relative to the acrylic polymer.

Through a slurry composition produced using the presently disclosedbinder composition, it is possible to form a solidelectrolyte-containing layer that can cause an all-solid-state secondarybattery to display excellent high-temperature cycle characteristics.

<Acrylic Polymer>

The acrylic polymer is a component that functions as a binder in a solidelectrolyte-containing layer that is formed from a slurry compositioncontaining the binder composition. Note that the presently disclosedbinder composition may include one acrylic polymer or may include two ormore acrylic polymers.

«Chemical Composition»

The acrylic polymer is a polymer that includes a (meth)acrylic acidester monomer unit as a repeating unit in a proportion of 50 mass % ormore as previously described. Note that the acrylic polymer may includerepeating units other than the (meth)acrylic acid ester monomer unit(hereinafter, referred to as “other repeating units”).

[(Meth)Acrylic Acid Ester Monomer Unit]

Examples of (meth)acrylic acid ester monomers that can form the(meth)acrylic acid ester monomer unit include, but are not specificallylimited to, (meth)acrylic acid alkyl ester monomers and (meth)acrylicacid alkoxyalkyl ester monomers. Note that one (meth)acrylic acid estermonomer may be used individually, or two or more (meth)acrylic acidester monomers may be used in combination.

Although no specific limitations are placed on (meth)acrylic acid alkylester monomers that can be used, an ester of (meth)acrylic acid and analkanol having a carbon number of not less than 1 and not more than 8 ispreferable. Specific examples include methyl (meth)acrylate, ethyl(meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate,n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-hexyl (meth)acrylate,2-ethylhexyl (meth)acrylate, and cyclohexyl (meth)acrylate. One of these(meth)acrylic acid alkyl ester monomers may be used individually, or twoor more of these (meth)acrylic acid alkyl ester monomers may be used incombination. Of these (meth)acrylic acid alkyl ester monomers, ethyl(meth)acrylate and n-butyl (meth)acrylate are preferable from aviewpoint of sufficiently improving high-temperature cyclecharacteristics of an all-solid-state secondary battery, with ethylacrylate and n-butyl acrylate being more preferable.

Although no specific limitations are placed on (meth)acrylic acidalkoxyalkyl ester monomers that can be used, an ester of (meth)acrylicacid and an alkoxyalkyl alcohol having a carbon number of not less than2 and not more than 8 is preferable. Specific examples includemethoxymethyl (meth)acrylate, ethoxymethyl (meth)acrylate,2-methoxyethyl (meth)acrylate, 2-ethoxyethyl (meth)acrylate,2-propoxyethyl (meth)acrylate, 2-butoxyethyl (meth)acrylate,3-methoxypropyl (meth)acrylate, and 4-methoxybutyl (meth)acrylate. Oneof these (meth)acrylic acid alkoxyalkyl ester monomers may be usedindividually, or two or more of these (meth)acrylic acid alkoxyalkylester monomers may be used in combination. Of these (meth)acrylic acidalkoxyalkyl ester monomers, 2-ethoxyethyl (meth)acrylate and2-methoxyethyl (meth)acrylate are preferable from a viewpoint ofsufficiently improving high-temperature cycle characteristics of anall-solid-state secondary battery, with 2-ethoxyethyl acrylate and2-methoxyethyl acrylate being particularly preferable.

The proportional content of the (meth)acrylic acid ester monomer unit inthe acrylic polymer is required to be 50 mass % or more from a viewpointof ensuring binding capacity of the acrylic polymer, and is preferably60 mass % or more, and more preferably 70 mass % or more. On the otherhand, the upper limit for the proportional content of the (meth)acrylicacid ester monomer unit in the acrylic polymer is not specificallylimited, and the proportional content of the (meth)acrylic acid estermonomer unit can be 100 mass % or less.

The acrylic polymer is preferably a polymer that includes a(meth)acrylic acid alkyl ester monomer unit as a (meth)acrylic acidester monomer unit in a proportion of not less than 30 mass % and notmore than 100 mass % from a viewpoint of sufficiently improvinghigh-temperature cycle characteristics of an all-solid-state secondarybattery.

Moreover, the acrylic polymer preferably includes both an ethyl acrylateunit and an n-butyl acrylate unit from a viewpoint of sufficientlyimproving high-temperature cycle characteristics of an all-solid-statesecondary battery.

[Other Repeating Units]

No specific limitations are placed on other repeating units so long asthey are repeating units derived from monomers that are copolymerizablewith a (meth)acrylic acid ester monomer such as described above, andexamples of other repeating units include an aromatic vinyl monomerunit, an α,β-ethylenically unsaturated nitrile monomer unit, and anacrylamide monomer unit. Note that one monomer that can form anotherrepeating unit may be used individually, or two or more monomers thatcan form other repeating units may be used in combination.

Examples of aromatic vinyl monomers that can form an aromatic vinylmonomer unit include styrene, α-methylstyrene, and divinylbenzene. Oneof these aromatic vinyl monomers may be used individually, or two ormore of these aromatic vinyl monomers may be used in combination.

Examples of α,β-ethylenically unsaturated nitrile monomers that can forman α,β-ethylenically unsaturated nitrile monomer unit includeacrylonitrile and methacrylonitrile. One of these α,β-ethylenicallyunsaturated nitrile monomers may be used individually, or two or more ofthese α,β-ethylenically unsaturated nitrile monomers may be used incombination.

Examples of acrylamide monomers that can form an acrylamide monomer unitinclude acrylamide and methacrylamide. One of these acrylamide monomersmay be used individually, or two or more of these acrylamide monomersmay be used in combination.

Besides the aromatic vinyl monomers, α,β-ethylenically unsaturatednitrile monomers, and acrylamide monomers described above, olefinicmonomers such as ethylene, vinyl acetate, propylene, butadiene, andisoprene can also be used to form other repeating units.

Of these examples, styrene, acrylonitrile, methacrylonitrile, ethylene,and vinyl acetate are preferable as monomers that can form otherrepeating units, and acrylonitrile, methacrylonitrile, and ethylene aremore preferable as monomers that can form other repeating units.

The proportional content of other repeating units in the acrylic polymeris 50 mass % or less, preferably 40 mass % or less, and more preferably30 mass % or less.

«Production Method»

Although no specific limitations are placed on the method by which theacrylic polymer is produced through polymerization of the monomersdescribed above, it is preferable that the acrylic polymer is producedby emulsion polymerization described further below in the “Productionmethod of binder composition” section. In other words, the acrylicpolymer is preferably a polymer produced by emulsion polymerization(i.e., an emulsion polymer).

<Phosphoric Acid Ester Emulsifier>

Although no specific limitations are placed on the phosphoric acid esteremulsifier, the phosphoric acid ester emulsifier is normally added to apolymerization reaction system in production of the acrylic polymerusing the monomers described above with the aim of ensuringpolymerization stability, for example, and normally remains in theobtained binder composition.

«Type»

The phosphoric acid ester emulsifier may be an alkyl phosphoric acidester salt or an alkyl ether phosphoric acid ester salt, for example,but is not specifically limited thereto.

Examples of alkyl phosphoric acid ester salts include potassiummonostearyl phosphate, potassium distearyl phosphate, potassiummonobehenyl phosphate, potassium dibehenyl phosphate, potassiummonocetyl phosphate, potassium dicetyl phosphate, potassium monolaurylphosphate, potassium dilauryl phosphate, potassium monooctyl phosphate,potassium dioctyl phosphate, sodium monostearyl phosphate, sodiumdistearyl phosphate, triethanolamine monostearyl phosphate,triethanolamine distearyl phosphate, diethanolamine monostearylphosphate, and diethanolamine distearyl phosphate.

Examples of alkyl ether phosphoric acid ester salts include potassiummono(polyoxyethylene stearyl ether) phosphate, potassiumdi(polyoxyethylene stearyl ether) phosphate, potassiummono(polyoxyethylene lauryl ether) phosphate, potassiumdi(polyoxyethylene lauryl ether) phosphate, sodium mono(polyoxyethylenestearyl ether) phosphate, sodium di(polyoxyethylene stearyl ether)phosphate, potassium mono(polyoxypropylene stearyl ether) phosphate, andpotassium di(polyoxypropylene stearyl ether) phosphate.

One of the alkyl phosphoric acid ester salts and alkyl ether phosphoricacid ester salts described above may be used individually, or two ormore of the alkyl phosphoric acid ester salts and alkyl ether phosphoricacid ester salts may be used in combination.

The content of the phosphoric acid ester emulsifier contained in thepresently disclosed binder composition is required to be not less than500 mass ppm and not more than 20,000 mass ppm relative to the acrylicpolymer, is preferably 800 mass ppm or more, and is preferably 15,000mass ppm or less, and more preferably 10,000 mass ppm or less.

The phosphoric acid ester emulsifier is normally added to apolymerization reaction system in production of the acrylic polymer withthe aim of ensuring polymerization stability, for example, as previouslydescribed, and, in this case, the phosphoric acid ester emulsifierunavoidably remains in the obtained binder composition (particularly inthe acrylic polymer). The inventors have revealed that adequatehigh-temperature cycle characteristics of an all-solid-state secondarybattery cannot be ensured when the amount of this phosphoric acid esteremulsifier is excessively large. In other words, it is not possible tocause an all-solid-state secondary battery to display excellenthigh-temperature cycle characteristics when the amount of the phosphoricacid ester emulsifier contained in the binder composition is more than20,000 mass ppm relative to the acrylic polymer. On the other hand, whenthe amount of the phosphoric acid ester emulsifier that is used isreduced in order to reduce the amount of the phosphoric acid esteremulsifier in the binder composition, polymerization stability cannot beensured, and the recovery rate of the acrylic polymer excessivelydecreases due to the polymerization conversion rate of monomerdecreasing and polymer becoming attached to a reactor or impeller.Excessive washing of the acrylic polymer in order to reduce the amountof the phosphoric acid ester emulsifier in the binder composition isalso burdensome in terms of production. Therefore, the content of thephosphoric acid ester emulsifier contained in the binder composition isrequired to be 500 mass ppm or more from a viewpoint of ensuringproduction efficiency of the binder composition.

Note that the content (residual amount) of the phosphoric acid esteremulsifier in the binder composition can be adjusted by altering thetype of phosphoric acid ester emulsifier used in production of theacrylic polymer, the additive amount of the phosphoric acid esteremulsifier that is added to the polymerization reaction system, and thewashing conditions of the acrylic polymer (binder composition).

Also note that the phosphoric acid ester emulsifier used in thepresently disclosed binder composition is advantageous in terms of easeof removal through subsequently described water washing compared to anemulsifier (sodium dodecylbenzenesulfonate, etc.) other than aphosphoric acid ester emulsifier.

«Other Components»

No specific limitations are placed on components other than the acrylicpolymer and the phosphoric acid ester emulsifier described above thatcan optionally be contained in the binder composition.

For example, the binder composition can contain an organic solvent asanother component. Examples of organic solvents that can be used includechain aliphatic hydrocarbons such as hexane; cyclic aliphatichydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbonssuch as toluene and xylene; ketones such as ethyl methyl ketone,cyclohexanone, and diisobutyl ketone; esters such as ethyl acetate,butyl acetate, γ-butyrolactone, and ε-caprolactone; acylonitriles suchas acetonitrile and propionitrile; ethers such as tetrahydrofuran,ethylene glycol diethyl ether, and n-butyl ether; alcohols such asmethanol, ethanol, isopropanol, ethylene glycol, and ethylene glycolmonomethyl ether; and amides such as N-methylpyrrolidone andN,N-dimethylformamide.

Of these examples, a non-polar organic solvent is preferably used as theorganic solvent from a viewpoint of inhibiting degradation of a solidelectrolyte and obtaining a solid electrolyte-containing layer havingexcellent ion conductivity, with the use of hexane or xylene as theorganic solvent being more preferable. Moreover, xylene is particularlypreferable from a viewpoint of further improving high-temperature cyclecharacteristics of an all-solid-state secondary battery.

One of the organic solvents described above may be used individually, ortwo or more of the organic solvents described above may be used as amixture.

Moreover, a component used in production of the binder compositiondescribed further below in the “Production method of binder composition”section may remain in the binder composition as another component, andany of the optional components described further below in the “Slurrycomposition for all-solid-state secondary battery” section may be addedto the binder composition as another component.

Examples of components that may be used in production of the bindercomposition include a coagulant. Note that the term “coagulant” as usedin the present disclosure refers to a substance that is added in orderto cause aggregation and coagulation of an acrylic polymer present in adispersed state in water and that instantly causes irreversiblecoagulation of particles of an acrylic polymer dispersed in water in anormal temperature region (for example, 15° C. to 30° C.).

A coagulant unavoidably remains in the obtained binder composition(particularly in the acrylic polymer) in a situation in which thesubsequently described “Production method of binder composition” isadopted, for example. The inventors have revealed that adequatehigh-temperature cycle characteristics of an all-solid-state secondarybattery cannot be ensured when the amount of this coagulant isexcessively large. On the other hand, when the additive amount of thecoagulant used to cause coagulation of the acrylic polymer in the waterdispersion is reduced or excessive washing of the acrylic polymer isperformed after coagulation with the aim of reducing the amount of thecoagulant, production efficiency of the binder composition is lost dueto the recovery rate of the acrylic polymer excessively decreasing, forexample.

From the viewpoints set forth above, the content of a coagulantcontained in the presently disclosed binder composition is preferably500 mass ppm or more, and more preferably 800 mass ppm or more relativeto the acrylic polymer, and is preferably 5,000 mass ppm or less, morepreferably 4,500 mass ppm or less, even more preferably 4,000 mass ppmor less, and particularly preferably 3,500 mass ppm or less relative tothe acrylic polymer.

Note that the content of a “coagulant” relative to an “acrylic polymer”referred to in the present disclosure can be determined by elementalanalysis.

Also note that the content (residual amount) of the coagulant in thebinder composition can be adjusted by altering the additive amount ofthe coagulant that is added to a water dispersion of the acrylic polymerand the washing conditions of the acrylic polymer (binder composition)after coagulation.

Specific examples of coagulants include, but are not specificallylimited to, metal salts having a valence of not less than 1 and not morethan 3. A metal salt having a valence of not less than 1 and not morethan 3 is a salt including a metal that forms a metal ion having avalence of not less than 1 and not more than 3 when the salt isdissolved in water. For example, the metal salt may be a salt of aninorganic acid selected from hydrochloric acid, nitric acid, sulfuricacid, and the like or an organic acid such as acetic acid with a metalselected from sodium, potassium, lithium, magnesium, calcium, zinc,titanium, manganese, iron, cobalt, nickel, aluminum, tin, and the like,without any specific limitations. Moreover, a hydroxide of any of thesemetals, or the like, can be used.

Specific examples of the metal salt having a valence of not less than 1and not more than 3 include metal chlorides such as sodium chloride,potassium chloride, lithium chloride, magnesium chloride, calciumchloride, zinc chloride, titanium chloride, manganese chloride, ironchloride, cobalt chloride, nickel chloride, aluminum chloride, and tinchloride; metal nitrates such as sodium nitrate, potassium nitrate,lithium nitrate, magnesium nitrate, calcium nitrate, zinc nitrate,titanium nitrate, manganese nitrate, iron nitrate, cobalt nitrate,nickel nitrate, aluminum nitrate, and tin nitrate; and metal sulfatessuch as sodium sulfate, potassium sulfate, lithium sulfate, magnesiumsulfate, calcium sulfate, zinc sulfate, titanium sulfate, manganesesulfate, iron sulfate, cobalt sulfate, nickel sulfate, aluminum sulfate,and tin sulfate. Of these metal salts, calcium chloride, sodiumchloride, magnesium chloride, zinc chloride, and metal sulfates arepreferable from a viewpoint of ensuring production efficiency of thebinder composition while also sufficiently improving high-temperaturecycle characteristics of an all-solid-state secondary battery, withmetal sulfates being more preferable, and sodium sulfate and magnesiumsulfate even more preferable. Note that one of these metal salts may beused individually, or a plurality of these metal salts may be used incombination.

<Production Method of Binder Composition>

Although no specific limitations are placed on the method by which thepresently disclosed binder composition set forth above is produced, thepresently disclosed binder composition is preferably produced, forexample, through steps of:

emulsion polymerizing monomer including a (meth)acrylic acid estermonomer in the presence of a phosphoric acid ester emulsifier to obtainan emulsion polymerization liquid containing an acrylic polymer and thephosphoric acid ester emulsifier (emulsion polymerization step);

adding a coagulant to the emulsion polymerization liquid to causecoagulation of the acrylic polymer and obtain hydrous crumbs thatcontain the acrylic polymer and the phosphoric acid ester emulsifier(coagulation step);

washing the hydrous crumbs (washing step); and

drying the hydrous crumbs after the washing (drying step).

Note that the method of producing the binder composition through theemulsion polymerization step, the coagulation step, the washing step,and the drying step described above may include steps other than theemulsion polymerization step, the coagulation step, the washing step,and the drying step (hereinafter, referred to as “other steps”).

«Emulsion Polymerization Step»

In the emulsion polymerization step, monomer such as the (meth)acrylicacid ester monomer described above is emulsion polymerized in thepresence of a phosphoric acid ester emulsifier to obtain an emulsionpolymerization liquid that contains an acrylic polymer and thephosphoric acid ester emulsifier (water dispersion of acrylic polymer).The emulsion polymerization method in the emulsion polymerization stepcan be any method using a polymerization initiator, a polymerizationinhibitor, and so forth in addition to a phosphoric acid esteremulsifier, for example, without any specific limitations, so long asmonomer such as the (meth)acrylic acid ester monomer can be polymerizedin the presence of the phosphoric acid ester emulsifier.

An alkyl phosphoric acid ester salt and/or an alkyl ether phosphoricacid ester salt such as previously described can suitably be used as thephosphoric acid ester emulsifier.

The amount of the phosphoric acid ester emulsifier that is used, interms of the total amount of the phosphoric acid ester emulsifier thatis used per 100 parts by mass of all monomer used in polymerization, ispreferably not less than 0.1 parts by mass and not more than 7 parts bymass, more preferably not less than 0.5 parts by mass and not more than5 parts by mass, and even more preferably not less than 1 part by massand not more than 4 parts by mass.

Examples of polymerization initiators that can be used include azocompounds such as azobisisobutyronitrile; organic peroxides such asdiisopropylbenzene hydroperoxide, cumene hydroperoxide, paramenthanehydroperoxide, and benzoyl peroxide; and inorganic peroxides such aspotassium persulfate, sodium persulfate, and ammonium persulfate. One ofthese polymerization initiators may be used individually, or two or moreof these polymerization initiators may be used in combination. Theamount of the polymerization initiator that is used per 100 parts bymass of all monomer used in polymerization is preferably not less than0.001 parts by mass and not more than 1.0 parts by mass.

Moreover, an organic peroxide or inorganic peroxide used as thepolymerization initiator is preferably used in combination with areducing agent as a redox polymerization initiator. Examples of reducingagents that can be used in combination include, but are not specificallylimited to, compounds including a metal ion that is in a reduced statesuch as ferrous sulfate, hexamethylenediaminetetraacetic acid ironsodium salt, and copper naphthenate; ascorbic acid (salt) such asascorbic acid, sodium ascorbate, and potassium ascorbate; erythorbicacid (salt) such as erythorbic acid, sodium erythorbate, and potassiumerythorbate; saccharides; sulfinic acid salts such as sodiumhydroxymethanesulfinate; sulfurous acid salts such as sodium sulfite,potassium sulfite, sodium hydrogen sulfite, aldehyde sodium hydrogensulfite, and potassium hydrogen sulfite; pyrosulfurous acid salts suchas sodium pyrosulfite, potassium pyrosulfite, sodium hydrogenpyrosulfite, and potassium hydrogen pyrosulfite; thiosulfuric acid saltssuch as sodium thiosulfate and potassium thiosulfate; phosphorous acid(salt) such as phosphorous acid, sodium phosphite, potassium phosphite,sodium hydrogen phosphite, and potassium hydrogen phosphite;pyrophosphorous acid (salt) such as pyrophosphorous acid, sodiumpyrophosphite, potassium pyrophosphite, sodium hydrogen pyrophosphite,and potassium hydrogen pyrophosphite; and sodium formaldehydesulfoxylate. One of these reducing agents may be used individually, ortwo or more of these reducing agents may be used in combination. Theamount of the reducing agent that is used per 100 parts by mass of thepolymerization initiator is preferably not less than 0.0003 parts bymass and not more than 0.4 parts by mass.

Note that in the present disclosure, “acid (salt)” is used to mean anacid and/or a salt of that acid.

Examples of polymerization inhibitors that can be used includehydroxylamine, hydroxylamine sulfate, diethylhydroxylamine,hydroxylamine sulfonic acid and alkali metal salts thereof, sodiumdimethyldithiocarbamate, and hydroquinone. The amount of thepolymerization inhibitor that is used is not specifically limited but ispreferably not less than 0.1 parts by mass and not more than 2 parts bymass per 100 parts by mass of all monomer used in polymerization.

The amount of water that is used is not specifically limited but ispreferably not less than 80 parts by mass and not more than 500 parts bymass, and more preferably not less than 100 parts by mass and not morethan 300 parts by mass per 100 parts by mass of all monomer used inpolymerization.

Note that a polymerization auxiliary material such as a molecular weightmodifier, a particle diameter modifier, a chelating agent, or an oxygenscavenger can be used in the emulsion polymerization as necessary. Knownexamples of these polymerization auxiliary materials can be used.

The emulsion polymerization can be performed by a batch method, asemi-batch method, or a continuous method, but is preferably performedby a semi-batch method. Specifically, it is preferable to adopt a methodin which a polymerization reaction is performed while continuouslyadding at least one of monomer used in polymerization, a polymerizationinitiator, and a reducing agent to the polymerization reaction system ina dropwise manner from the start of the polymerization reaction until afreely selected period of time has elapsed, such as a method in which apolymerization reaction is performed while continuously adding monomerused in polymerization to a reaction system containing a polymerizationinitiator and a reducing agent in a dropwise manner from the start ofthe polymerization reaction until a freely selected period of time haselapsed. Moreover, it is more preferable that a polymerization reactionis performed while continuously adding each of monomer used inpolymerization, a polymerization initiator, and a reducing agent to thepolymerization reaction system in a dropwise manner from the start ofthe polymerization reaction until a freely selected period of time haselapsed. By performing a polymerization reaction while continuouslyadding these materials in a dropwise manner, emulsion polymerization canbe stably performed, which enables improvement of the polymerizationreaction rate. The polymerization is normally performed in a temperaturerange of not lower than 0° C. and not higher than 70° C., and preferablyin a temperature range of not lower than 5° C. and not higher than 50°C.

Moreover, in a case in which a polymerization reaction is performedwhile continuously adding monomer used in polymerization in a dropwisemanner, it is preferable that the monomer used in polymerization ismixed with an emulsifier and water such as to be in the form of amonomer emulsion and is then continuously added dropwise while in theform of a monomer emulsion. Although no specific limitations are placedon the method by which the monomer emulsion is produced, it may be amethod in which all of the monomer used in polymerization, all of theemulsifier, and water are stirred using a stirrer such as a Homo Mixeror a disc turbine, for example. The amount of water that is used in themonomer emulsion per 100 parts by mass of all monomer used inpolymerization is preferably not less than 10 parts by mass and not morethan 70 parts by mass, and more preferably not less than 20 parts bymass and not more than 50 parts by mass.

Furthermore, in a case in which a polymerization reaction is performedwhile continuously adding each of monomer used in polymerization, apolymerization initiator, and a reducing agent to the polymerizationreaction system in a dropwise manner from the start of thepolymerization reaction until a freely selected period of time haselapsed, the monomer, the polymerization initiator, and the reducingagent may be added dropwise to the polymerization system from separatedripping devices to one another, or at least the polymerizationinitiator and the reducing agent may be premixed and may be addeddropwise to the polymerization system from the same dripping device inthe form of an aqueous solution as necessary. The reaction may becontinued for a freely selected period of time after completion of thedropwise addition in order to improve the polymerization reaction rate.

«Coagulation Step»

In the coagulation step, a coagulant is added to the emulsionpolymerization liquid that has been obtained in the emulsionpolymerization step described above to cause coagulation of the acrylicpolymer and obtain hydrous crumbs (coagulated material containing atleast the acrylic polymer, phosphoric acid ester emulsifier, and water).

A metal salt having a valence of not less than 1 and not more than 3such as previously described can suitably be used as the coagulant. Theamount of the coagulant that is used per 100 parts by mass of theacrylic polymer in the emulsion polymerization liquid is preferably notless than 1 part by mass and not more than 20 parts by mass, and morepreferably not less than 2 parts by mass and not more than 15 parts bymass from a viewpoint of causing the content (residual amount) of thecoagulant in the finally obtained acrylic polymer to be within any ofthe previously described ranges.

The coagulation temperature is not specifically limited but ispreferably not lower than 50° C. and not higher than 90° C., and morepreferably not lower than 60° C. and not higher than 80° C.

«Washing Step»

In the washing step, the hydrous crumbs that have been obtained in thecoagulation step described above are washed. By washing the hydrouscrumbs, the residual amounts of components (phosphoric acid esteremulsifier, coagulant, etc.) other than the acrylic polymer can bereduced.

The method of washing is not specifically limited and may be a methodthat uses water as a washing liquid and in which the hydrous crumbs aremixed with water that has been added thereto to perform water washing.The temperature during water washing is not specifically limited but ispreferably not lower than 5° C. and not higher than 60° C., and morepreferably not lower than 10° C. and not higher than 50° C. Moreover,the mixing time is not specifically limited but is preferably not lessthan 1 minute and not more than 60 minutes, and more preferably not lessthan 2 minutes and not more than 30 minutes.

Although no specific limitations are placed on the amount of water thatis added to the hydrous crumbs in water washing, from a viewpoint thatthe contents (residual amounts) of components other than the acrylicpolymer in the finally obtained binder composition can be effectivelyreduced, the amount of water that is added per 100 parts by mass of theacrylic polymer contained in the hydrous crumbs is preferably not lessthan 150 parts by mass and not more than 9,800 parts by mass, and morepreferably not less than 150 parts by mass and not more than 1,800 partsby mass.

No specific limitations are placed on the number of water washes, andalthough washing may be performed just once, it is preferable thatwashing is performed not fewer than 2 times and not more than 10 times,and more preferably not fewer than 3 times and not more than 8 timesfrom a viewpoint of reducing the contents (residual amounts) ofcomponents other than the acrylic polymer in the finally obtained bindercomposition. Note that although a larger number of water washes isdesirable from a viewpoint of reducing the contents (residual amounts)of components other than the acrylic polymer in the finally obtainedbinder composition, performing washing in excess of any of the rangesset forth above only has a small effect in terms of removing componentsother than the acrylic polymer but has a significant influence onreducing production efficiency due to increasing the number of steps.Therefore, the number of washes is preferably set within any of theranges set forth above.

Furthermore, water washing in the washing step may be followed by acidwashing using an acid as a washing liquid.

«Drying Step»

In the drying step, the hydrous crumbs that have undergone the washingstep set forth above are dried to obtain a coagulated and dried materialthat contains at least the acrylic polymer and the phosphoric acid esteremulsifier.

Examples of drying methods that can be used in the drying step include,but are not specifically limited to, methods in which drying isperformed using a dryer such as a screw-type extruder, a kneader-typedryer, an expander-dryer, a hot-air dryer, or a vacuum dryer. Moreover,a drying method that is a combination of these methods may be adopted.Furthermore, the hydrous crumbs may be subjected to separation byfiltration using a sieve such as a rotary screen or a shaker screen; acentrifugal dehydrator; or the like, as necessary, prior to performingdrying in the drying step.

The drying temperature in the drying step is not specifically limitedand differs depending on the dryer used in drying. For example, in acase in which a hot-air dryer is used, the drying temperature ispreferably not lower than 80° C. and not higher than 200° C., and morepreferably not lower than 100° C. and not higher than 170° C.

«Other Steps»

No specific limitations are placed on other steps that can be includedin the production method of the binder composition set forth above.

For example, the coagulated and dried material that is obtained in thedrying step set forth above may be used in that form as the bindercomposition, or a step of adding an organic solvent to the coagulatedand dried material (organic solvent addition step) may be performedafter the drying step, and a liquid composition that contains theacrylic polymer, the phosphoric acid ester emulsifier, and the organicsolvent may be used as the binder composition.

(Slurry Composition for all-Solid-State Secondary Battery)

The presently disclosed slurry composition contains a solid electrolyteand the organic solvent-containing binder composition set forth above.In other words, the presently disclosed slurry composition is acomposition in which at least a solid electrolyte, the previouslydescribed acrylic polymer, and the previously described phosphoric acidester emulsifier are dispersed and/or dissolved in an organic solvent.

As a result of the presently disclosed slurry composition being producedusing the presently disclosed binder composition set forth above, it ispossible to form a solid electrolyte-containing layer that can cause anall-solid-state secondary battery to display excellent high-temperaturecycle characteristics through the slurry composition.

Note that in a case in which the presently disclosed slurry compositionfor an all-solid-state secondary battery is to be used to form anelectrode mixed material layer (i.e., in a case in which the slurrycomposition is a slurry composition for an all-solid-state secondarybattery electrode), the presently disclosed slurry composition for anall-solid-state secondary battery normally contains at least a solidelectrolyte, an electrode active material, an acrylic polymer, aphosphoric acid ester emulsifier, and an organic solvent.

Moreover, in a case in which the presently disclosed slurry compositionfor an all-solid-state secondary battery is to be used to form a solidelectrolyte layer (i.e., in a case in which the slurry composition is aslurry composition for an all-solid-state secondary battery solidelectrolyte layer), the presently disclosed slurry composition for anall-solid-state secondary battery normally contains at least a solidelectrolyte, an acrylic polymer, a phosphoric acid ester emulsifier, andan organic solvent, and does not contain an electrode active material.

<Solid Electrolyte>

Although inorganic solid electrolytes and organic solid electrolytes canboth be used as the solid electrolyte, an inorganic solid electrolytecan suitably be used.

The inorganic solid electrolyte may be a crystalline inorganic ionconductor, an amorphous inorganic ion conductor, or a mixture thereofwithout any specific limitations. In a case in which the all-solid-statesecondary battery is an all-solid-state lithium ion secondary battery,for example, a crystalline inorganic lithium ion conductor, an amorphousinorganic lithium ion conductor, or a mixture thereof can normally beused as the inorganic solid electrolyte. In particular, the inorganicsolid electrolyte preferably includes a sulfide inorganic solidelectrolyte from a viewpoint of enhancing battery performance, such ashigh-temperature cycle characteristics.

Although the following describes, as one example, a case in which theslurry composition for an all-solid-state secondary battery is a slurrycomposition for an all-solid-state lithium ion secondary battery, thepresently disclosed slurry composition for an all-solid-state secondarybattery is not limited to the following example.

Examples of crystalline inorganic lithium ion conductors include Li₃N,LISICON (Li₁₄Zn(GeO₄)₄), perovskite-type Li_(0.5)La_(0.5)TiO₃,garnet-type Li₇La₃Zr₂O₁₀, LIPON (Li_(3+y)PO_(4−x)N_(x)), andThio-LISICON (Li_(3.25)Ge_(0.25)P_(0.75)S₄).

One of the crystalline inorganic lithium ion conductors described abovemay be used individually, or two or more of the crystalline inorganiclithium ion conductors may be used as a mixture.

The amorphous inorganic lithium ion conductor is not specificallylimited so long as it contains a sulfur atom and displays ionconductivity and may be glass Li—Si—S—O, Li—P—S, or a product obtainedusing a raw material composition that contains Li₂S and a sulfide of anelement belonging to groups 13 to 15 of the periodic table.

The element belonging to groups 13 to 15 can be Al, Si, Ge, P, As, Sb,or the like, for example. More specifically, the sulfide of an elementbelonging to groups 13 to 15 may be Al₂S₃, SiO₂, GeS₂, P₂S₃, P₂S₅,As₂S₃, Sb₂S₃, or the like. The method by which an amorphous inorganiclithium ion conductor is synthesized using the raw material compositioncan be an amorphization method such as mechanical milling or meltquenching. The amorphous inorganic lithium ion conductor that is formedusing a raw material composition containing Li₂S and a sulfide of anelement belonging to groups 13 to 15 of the periodic table is preferablyLi₂S—P₂S₅, Li₂S—SiO₂, Li₂S—GeS₂, or Li₂S—Al₂S₃, and more preferablyLi₂S—P₂S₅.

One of the amorphous inorganic lithium ion conductors described abovemay be used individually, or two or more of the amorphous inorganiclithium ion conductors may be used as a mixture.

Of the inorganic solid electrolytes described above, an amorphousinorganic lithium ion conductor is preferable as an inorganic solidelectrolyte for an all-solid-state lithium ion secondary battery from aviewpoint of enhancing battery performance, such as high-temperaturecycle characteristics, with an amorphous sulfide containing Li and Pbeing more preferable. An amorphous sulfide containing Li and P has highlithium ion conductivity, and thus can reduce internal resistance andimprove output characteristics of a battery in which the amorphoussulfide is used as an inorganic solid electrolyte.

The amorphous sulfide containing Li and P is more preferably sulfideglass formed of Li₂S and P₂S₅ from a viewpoint of reducing internalresistance and improving output characteristics of a battery, withsulfide glass produced from a mixed raw material of Li₂S and P₂S₅ inwhich the molar ratio of Li₂S:P₂S₅ is 65:35 to 85:15 being particularlypreferable. Moreover, the amorphous sulfide containing Li and P ispreferably sulfide glass-ceramic obtained by reacting a mixed rawmaterial of Li₂S and P₂S₅ in which the molar ratio of Li₂S:P₂S₅ is 65:35to 85:15 by a mechanochemical method. From a viewpoint of maintaining astate of high lithium ion conductivity, the molar ratio of Li₂S:P₂S₅ inthe mixed raw material is preferably 68:32 to 80:20.

Note that the inorganic solid electrolyte may contain one or moresulfides selected from the group consisting of Al₂S₃, B₂S₃, and SiS₂ asa starting material other than Li₂S and P₂S₅ to the extent that ionconductivity is not reduced. The addition of such a sulfide canstabilize a glass component in the inorganic solid electrolyte.

In the same manner, the inorganic solid electrolyte may contain one ormore ortho-oxoacid lithium salts selected from the group consisting ofLi₃PO₄, Li₄SiO₄, Li₄GeO₄, Li₃BO₃, and Li₃AlO₃, in addition to Li₂S andP₂S₅. The inclusion of such an ortho-oxoacid lithium salt can stabilizea glass component in the inorganic solid electrolyte.

<Acrylic Polymer>

The acrylic polymer is the acrylic polymer that was contained in thebinder composition and, more specifically, can be any of the examplesdescribed above in the “Binder composition for all-solid-state secondarybattery” section.

Note that in the slurry composition, a binder may be dissolved in theorganic solvent or may be dispersed in a particulate form or the like,for example, without dissolving in the organic solvent.

The amount of the acrylic polymer that is contained in the slurrycomposition for an all-solid-state secondary battery is not specificallylimited but is preferably 0.05 parts by mass or more, more preferably0.1 parts by mass or more, and even more preferably 0.2 parts by mass ormore per 100 parts by mass of the solid electrolyte, and is preferably 5parts by mass or less, more preferably 3 parts by mass or less, and evenmore preferably 2 parts by mass or less per 100 parts by mass of thesolid electrolyte. When the amount of the acrylic polymer is not lessthan any of the lower limits set forth above, a solidelectrolyte-containing layer can be well formed. Moreover, when theamount of the acrylic polymer is not more than any of the upper limitsset forth above, reduction of ion conductivity of a solidelectrolyte-containing layer can be inhibited.

<Phosphoric Acid Ester Emulsifier>

The phosphoric acid ester emulsifier is the phosphoric acid esteremulsifier that was contained in the binder composition and, morespecifically, can be any of the examples described above in the “Bindercomposition for all-solid-state secondary battery” section.

Note that the content of the phosphoric acid ester emulsifier relativeto the acrylic polymer in the presently disclosed slurry composition isthe same as the content of the phosphoric acid ester emulsifier relativeto the acrylic polymer in the presently disclosed binder composition setforth above because the phosphoric acid ester emulsifier originates fromthe binder composition as previously described.

<Organic Solvent>

The organic solvent can be any of the examples described above in the“Binder composition for all-solid-state secondary battery” section.

Note that the organic solvent contained in the slurry composition may bejust organic solvent that was contained in the binder composition or mayinclude organic solvent that was separately added during production ofthe slurry composition.

<Electrode Active Material>

The electrode active material is a material that gives and receiveselectrons in an electrode of an all-solid-state secondary battery. In acase in which the all-solid-state secondary battery is anall-solid-state lithium ion secondary battery, for example, theelectrode active material is normally a material that can occlude andrelease lithium.

Although the following describes, as one example, a case in which theslurry composition for an all-solid-state secondary battery is a slurrycomposition for an all-solid-state lithium ion secondary battery, thepresently disclosed slurry composition for an all-solid-state secondarybattery is not limited to the following example.

A positive electrode active material for an all-solid-state lithium ionsecondary battery may be a positive electrode active material formed ofan inorganic compound or a positive electrode active material formed ofan organic compound without any specific limitations. Also note that thepositive electrode active material may be a mixture of an inorganiccompound and an organic compound.

Examples of positive electrode active materials formed of inorganiccompounds include transition metal oxides, complex oxides of lithium anda transition metal (lithium-containing complex metal oxides), andtransition metal sulfides. The aforementioned transition metal may beFe, Co, Ni, Mn, or the like. Specific examples of inorganic compoundsthat can be used as the positive electrode active material includelithium-containing complex metal oxides such as LiCoO₂ (lithium cobaltoxide), LiNiO₂, LiMnO₂, LiMn₂O₄, LiFePO₄, and LiFeVO₄; transition metalsulfides such as TiS₂, TiS₃, and amorphous MoS₂; and transition metaloxides such as Cu₂V₂O₃, amorphous V₂O—P₂O₅, MoO₃, V₂O₅, and V₆O₁₃. Thesecompounds may have undergone partial element substitution.

One of the positive electrode active materials formed of inorganiccompounds described above may be used individually, or two or more ofthe positive electrode active materials formed of inorganic compoundsmay be used as a mixture.

Examples of positive electrode active materials formed of organiccompounds include polyaniline, polypyrrole, polyacenes, disulfidecompounds, polysulfide compounds, and N-fluoropyridinium salts.

One of the positive electrode active materials formed of organiccompounds described above may be used individually, or two or more ofthe positive electrode active materials formed of organic compounds maybe used as a mixture.

A negative electrode active material for an all-solid-state lithium ionsecondary battery may be an allotrope of carbon such as graphite orcoke. Note that a negative electrode active material formed of anallotrope of carbon can be used in a mixed or coated form with a metal,a metal salt, an oxide, or the like. Examples of negative electrodeactive materials that can be used also include oxides and sulfates ofsilicon, tin, zinc, manganese, iron, nickel, and the like; lithiummetal; lithium alloys such as Li—Al, Li—Bi—Cd, and Li—Sn—Cd; lithiumtransition metal nitrides; and silicone.

One of the negative electrode active materials described above may beused individually, or two or more of the negative electrode activematerials described above may be used as a mixture.

<Optional Components>

The presently disclosed slurry composition may contain components otherthan the solid electrolyte, acrylic polymer, phosphoric acid esteremulsifier, organic solvent, and electrode active material describedabove.

Examples of such optional components include coagulants, known bindersother than the acrylic polymer, conductive materials, dispersants,leveling agents, defoamers, and reinforcing materials. In a case inwhich the all-solid-state secondary battery is an all-solid-statelithium ion secondary battery, for example, a lithium salt can becontained as another component. These other components are notspecifically limited so long as they do not influence battery reactions.

The coagulant is a coagulant that was contained in the bindercomposition and, more specifically, can be any of the examples describedabove in the “Binder composition for all-solid-state secondary battery”section.

Note that the content of the coagulant relative to the acrylic polymerin the presently disclosed slurry composition is the same as the contentof the coagulant relative to the acrylic polymer in the presentlydisclosed binder composition set forth above because the coagulantoriginates from the binder composition as previously described.

Examples of known binders other than the acrylic polymer that can beused include macromolecular compounds such as fluoropolymers, dienepolymers, and nitrile polymers. One of these macromolecular compoundsmay be used individually, or a plurality of these macromolecularcompounds may be used in combination. Examples of fluoropolymers, dienepolymers, and nitrile polymers that can be used include fluoropolymers,diene polymers, nitrile polymers, and so forth that are described inJP2012-243476A.

A conductive material is a material for ensuring electrical contactamong an electrode active material in an electrode mixed material layerformed using the slurry composition for an all-solid-state secondarybattery (i.e., a slurry composition for an all-solid-state secondarybattery electrode). Examples of conductive materials that can be usedinclude conductive carbon materials such as carbon black (for example,acetylene black, Ketjenblack® (Ketjenblack is a registered trademark inJapan, other countries, or both), and furnace black), single-walled ormulti-walled carbon nanotubes (multi-walled carbon nanotubes areinclusive of cup-stacked carbon nanotubes), carbon nanohorns, vaporgrown carbon fiber, milled carbon fiber obtained by pyrolyzing and thenpulverizing polymer fiber, single layer or multilayer graphene, andcarbon nonwoven fabric sheet obtained through pyrolysis of nonwovenfabric made from polymer fiber; and fibers and foils of various metals.

One of such conductive materials may be used individually, or two ormore of such conductive materials may be used in combination.

Examples of lithium salts, dispersants, leveling agents, defoamers, andreinforcing materials that can be used include, but are not specificallylimited to, those described in JP2012-243476A.

<Production Method of Slurry Composition>

Although no specific limitations are placed on the method by which thepresently disclosed slurry composition set forth above is produced, theslurry composition can be obtained by mixing a binder compositionproduced by the procedure described above in the “Production method ofbinder composition” section, a solid electrolyte, and an electrodeactive material and optional components that are added as necessary, inthe presence of an organic solvent.

(Solid Electrolyte-Containing Layer)

The presently disclosed solid electrolyte-containing layer is a layerthat contains a solid electrolyte and may, for example, be an electrodemixed material layer (positive electrode mixed material layer ornegative electrode mixed material layer) that gives and receiveselectrons through electrochemical reactions or a solid electrolyte layerthat is provided between a positive electrode mixed material layer and anegative electrode mixed material layer that are in opposition to eachother.

Moreover, the presently disclosed solid electrolyte-containing layer isa layer that is formed using the slurry composition for anall-solid-state secondary battery set forth above and can be formed by,for example, applying the slurry composition set forth above onto thesurface of a suitable substrate to form a coating film, and then dryingthe coating film that is formed. In other words, the presently disclosedsolid electrolyte-containing layer is formed of a dried product of theslurry composition set forth above and normally contains at least asolid electrolyte, an acrylic polymer, and a phosphoric acid esteremulsifier. Note that components contained in the solidelectrolyte-containing layer are components that were contained in theslurry composition, and thus the content ratio of these components isnormally the same as the content ratio thereof in the slurrycomposition.

The presently disclosed solid electrolyte-containing layer can cause anall-solid-state secondary battery to display excellent high-temperaturecycle characteristics as a result of being formed from the presentlydisclosed slurry composition for an all-solid-state secondary battery.

<Substrate>

No limitations are placed on the substrate onto which the slurrycomposition is applied. For example, a coating film of the slurrycomposition may be formed on the surface of a releasable substrate, thecoating film may be dried to form a solid electrolyte-containing layer,and then the releasable substrate may be peeled from the solidelectrolyte-containing layer. The solid electrolyte-containing layerthat is peeled from the releasable substrate in this manner can be usedas a free-standing film in formation of a battery member (for example,an electrode or a solid electrolyte layer) of an all-solid-statesecondary battery.

However, it is preferable that a current collector or an electrode isused as the substrate from a viewpoint of increasing battery memberproduction efficiency since a step of peeling the solidelectrolyte-containing layer can be omitted. Specifically, the slurrycomposition is preferably applied onto a current collector serving as asubstrate when an electrode mixed material layer is to be produced.Moreover, the slurry composition is preferably applied onto an electrode(positive electrode or negative electrode) when a solid electrolytelayer is to be produced.

«Current Collector»

The current collector is a material having electrical conductivity andelectrochemical durability. Specifically, the current collector may, forexample, be made of iron, copper, aluminum, nickel, stainless steel,titanium, tantalum, gold, platinum, or the like. Of these materials,copper foil is particularly preferable as a current collector used for anegative electrode. On the other hand, aluminum foil is particularlypreferable as a current collector used for a positive electrode. One ofthese materials may be used individually, or two or more of thesematerials may be used in combination in a freely selected ratio.

«Electrode»

The electrode (positive electrode or negative electrode) is notspecifically limited and may be an electrode that includes an electrodemixed material layer containing an electrode active material, a solidelectrolyte, and a binder that is formed on a current collector such asdescribed above.

Known electrode active materials, solid electrolytes, and binders can beused as the electrode active material, the solid electrolyte, and thebinder that are contained in the electrode mixed material layer of theelectrode without any specific limitations. Note that the electrodemixed material layer of the electrode may be a layer that corresponds tothe presently disclosed solid electrolyte-containing layer.

<Formation Method of Solid Electrolyte-Containing Layer>

Examples of methods by which the solid electrolyte-containing layer maybe formed on a substrate such as the current collector or electrodedescribed above include:

(1) a method in which the presently disclosed slurry composition isapplied onto the surface of a substrate (surface at the electrode mixedmaterial layer side in the case of an electrode; same applies below) andis then dried;

(2) a method in which a substrate is immersed in the presently disclosedslurry composition and is then dried; and

(3) a method in which the presently disclosed slurry composition isapplied onto a releasable substrate and is dried to produce a solidelectrolyte-containing layer that is then transferred onto the surfaceof an electrode or the like.

Of these methods, method (1) is particularly preferable since it allowssimple control of the thickness of the solid electrolyte-containinglayer. In more detail, method (1) includes a step of applying the slurrycomposition onto a substrate (application step) and a step of drying theslurry composition that has been applied onto the substrate to form asolid electrolyte-containing layer (solid electrolyte-containing layerformation step).

«Application Step»

Examples of methods by which the slurry composition may be applied ontothe substrate in the application step include, but are not specificallylimited to, methods such as doctor blading, reverse roll coating, directroll coating, gravure coating, extrusion coating, and brush coating.

«Solid Electrolyte-Containing Layer Formation Step»

Commonly known methods can be adopted without any specific limitationsas the method by which the slurry composition on the substrate is driedin the solid electrolyte-containing layer formation step. Examples ofdrying methods that may be used include drying by warm, hot, orlow-humidity air, drying in a vacuum, and drying by irradiation withinfrared light, electron beams, or the like.

Note that in a case in which the solid electrolyte-containing layer isan electrode mixed material layer, a pressing process is preferablyperformed by roll pressing or the like after drying. By performing apressing process, the obtained electrode mixed material layer can befurther densified.

(Electrode)

An electrode that is obtained by forming an electrode mixed materiallayer on a current collector using the presently disclosed slurrycomposition for an all-solid-state secondary battery includes anelectrode mixed material layer that contains at least a solidelectrolyte, an acrylic polymer, a phosphoric acid ester emulsifier, andan electrode active material and can cause an all-solid-state secondarybattery to display excellent high-temperature cycle characteristics.

(Solid Electrolyte Layer)

A solid electrolyte layer that is formed using the presently disclosedslurry composition for an all-solid-state secondary battery contains atleast a solid electrolyte, an acrylic polymer, and a phosphoric acidester emulsifier and can cause an all-solid-state secondary battery todisplay excellent high-temperature cycle characteristics.

(All-Solid-State Secondary Battery)

The presently disclosed all-solid-state secondary battery normallyincludes a positive electrode, a solid electrolyte layer, and a negativeelectrode, and a feature thereof is that at least one of a positiveelectrode mixed material layer of the positive electrode, a negativeelectrode mixed material layer of the negative electrode, and the solidelectrolyte layer is the presently disclosed solidelectrolyte-containing layer. In other words, the presently disclosedall-solid-state secondary battery includes at least one of: a positiveelectrode including a positive electrode mixed material layer formedusing a slurry composition for an all-solid-state secondary batterypositive electrode serving as the presently disclosed slurry compositionfor an all-solid-state secondary battery; a negative electrode includinga negative electrode mixed material layer formed using a slurrycomposition for an all-solid-state secondary battery negative electrodeserving as the presently disclosed slurry composition for anall-solid-state secondary battery; and a solid electrolyte layer formedusing a slurry composition for an all-solid-state secondary batterysolid electrolyte layer serving as the presently disclosed slurrycomposition for an all-solid-state secondary battery.

The presently disclosed all-solid-state secondary battery has excellentbattery performance, such as high-temperature cycle characteristics, asa result of including the presently disclosed solidelectrolyte-containing layer.

Note that any electrode for an all-solid-state secondary batteryincluding an electrode mixed material layer that does not correspond tothe presently disclosed solid electrolyte-containing layer can be usedwithout any specific limitations in the presently disclosedall-solid-state secondary battery as an electrode for an all-solid-statesecondary battery including an electrode mixed material layer that doesnot correspond to the presently disclosed solid electrolyte-containinglayer.

Moreover, any solid electrolyte layer, such as a solid electrolyte layerdescribed in JP2012-243476A, JP2013-143299A, or JP2016-143614A, forexample, can be used without any specific limitations in the presentlydisclosed all-solid-state secondary battery as a solid electrolyte layerthat does not correspond to the presently disclosed solidelectrolyte-containing layer.

The presently disclosed all-solid-state secondary battery can beobtained by stacking the positive electrode and the negative electrodesuch that the positive electrode mixed material layer of the positiveelectrode and the negative electrode mixed material layer of thenegative electrode are in opposition via the solid electrolyte layer andoptionally performing pressing thereof to obtain a laminate,subsequently placing the laminate in a battery container in that form orafter rolling, folding, or the like, depending on the battery shape, andthen sealing the battery container. Note that pressure increase insidethe battery and the occurrence of overcharging or overdischarging can beprevented by placing an expanded metal, an overcurrent preventing devicesuch as a fuse or a PTC device, a lead plate, or the like in the batterycontainer as necessary. The shape of the battery may be a coin type,button type, sheet type, cylinder type, prismatic type, flat type, orthe like.

EXAMPLES

The following provides a more specific description of the presentdisclosure based on examples. However, the present disclosure is notlimited to the following examples. In the following description, “%” and“parts” used in expressing quantities are by mass, unless otherwisespecified.

In the examples and comparative examples, the following methods wereused to measure and evaluate the content of an emulsifier and thecontent of a coagulant in a binder composition, the recovery rate of anacrylic polymer, and the high-temperature cycle characteristics of anall-solid-state secondary battery.

<Content of Emulsifier>

A binder composition (coagulated and dried material) was dissolved intetrahydrofuran and was then subjected to GPC measurement withtetrahydrofuran as an eluent solvent in order to measure the residualamount of an emulsifier, such as a phosphoric acid ester emulsifier, inthe binder composition. Specifically, an integrated value for a peakcorresponding to the molecular weight of an emulsifier used inproduction was determined from a chart obtained through the GPCmeasurement, this integrated value and an integrated value for a peakattributed to an acrylic polymer were compared, and a mass ratio wasdetermined from these integrated values and the corresponding molecularweights to calculate the residual amount of the emulsifier.

<Content of Coagulant>

Elemental analysis of a binder composition (coagulated and driedmaterial) was performed by inductively coupled plasma atomic emissionspectroscopy (ICP-AES) to measure the content of a coagulant in thecoagulated and dried material. Specifically, elemental analysis wasperformed to determine the proportional content of a constituent elementof a used coagulant in the binder composition, and then the content ofthe coagulant was calculated from the determined proportional content.

<Recovery Rate of Acrylic Polymer>

The amount of an acrylic polymer that could be recovered as a bindercomposition was calculated as a proportion relative to the theoreticalyield assumed from the total amount of charged monomers and thepolymerization conversion rate, and this proportion was taken to be therecovery rate (%).

<High-Temperature Cycle Characteristics>

A produced all-solid-state secondary battery was used to performcharge/discharge cycling at 25° C. in which the all-solid-statesecondary battery was charged to 4.2 V with a constant current andsubsequently charged with a constant voltage by a 0.1C constantcurrent-constant voltage charging method, and was then discharged to 3.0V with a 0.1C constant current. Five charge/discharge cycles wereperformed, and the discharge capacity of the 5th cycle was taken to bethe initial capacity C₅. The all-solid-state secondary battery was thenused to perform a charge/discharge cycling test in the same manner in an80° C. thermostatic tank, and the discharge capacity C₂₀ of the 20^(th)cycle, the discharge capacity C₅₀ of the 50^(th) cycle, and thedischarge capacity C₁₀₀ of the 100^(th) cycle were each measured. Acapacity maintenance rate for the all-solid-state secondary battery ateach of these numbers of cycles (C₂₀/C₅×100%; C₅₀/C₅×100%; C₁₀₀/C₅×100%)was calculated. A higher capacity maintenance rate indicates that theall-solid-state secondary battery has better high-temperature cyclecharacteristics.

Example 1 <Production of Binder Composition> «Emulsion PolymerizationStep»

A mixing vessel including a Homo Mixer was charged with 45.48 parts ofpure water, 50 parts of ethyl acrylate and 50 parts of n-butyl acrylateas (meth)acrylic acid ester monomers (proportions among all monomers:50% ethyl acrylate and 50% n-butyl acrylate), and 2.5 parts of sodiummonostearyl phosphate as a phosphoric acid ester emulsifier, and thesematerials were stirred to obtain a monomer emulsion.

Next, 170 parts of pure water and 2.98 parts of the monomer emulsionobtained as described above were loaded into a polymerization reactiontank including a thermometer and a stirrer, and were cooled to atemperature of 12° C. under a stream of nitrogen. Thereafter, 145 partsof the monomer emulsion obtained as described above, 0.00033 parts offerrous sulfate and 0.264 parts of sodium ascorbate as reducing agents,and 7.72 parts of a 2.85% potassium persulfate aqueous solution (0.22parts in terms of potassium persulfate) as a polymerization initiatorwere continuously added dropwise into the polymerization reaction tankover 3 hours. The reaction was then continued for 1 hour in a state inwhich the internal temperature of the polymerization reaction tank washeld at 23° C., and once the polymerization conversion rate wasconfirmed to have reached 95%, the polymerization reaction was endedthrough addition of hydroquinone as a polymerization inhibitor to yieldan emulsion polymerization liquid.

«Coagulation Step»

The emulsion polymerization liquid obtained in the emulsionpolymerization step was transferred to a coagulation tank, and 60 partsof deionized water was added to 100 parts of the emulsion polymerizationliquid to obtain a mixture. The mixture was heated to 85° C. and wasthen stirred at a temperature of 85° C. while 3.3 parts of sodiumsulfate (11 parts per 100 parts of acrylic polymer contained in mixture)as a coagulant was continuously added thereto to cause coagulation ofthe acrylic polymer and obtain hydrous crumbs of the acrylic polymer.

«Washing Step»

After adding 200 parts of deionized water relative to 100 parts of solidcontent of the hydrous crumbs obtained in the coagulation step, 5minutes of stirring was performed at 15° C. inside the coagulation tank,and then water was discharged from the coagulation tank to perform waterwashing of the hydrous crumbs. This water washing was repeated fourtimes in total.

«Drying Step»

The hydrous crumbs that had undergone water washing in the washing stepwere then dried at 110° C. for 1 hour in a hot-air dryer to obtain acoagulated and dried material. This coagulated and dried material(binder composition) was used to measure the contents of the emulsifierand the coagulant and the recovery rate of the acrylic polymer. Theresults are shown in Table 1. The acrylic polymer was confirmed toinclude 50.1% of ethyl acrylate units and 49.9% of n-butyl acrylateunits by NMR measurement. Note that the proportion constituted by eachmonomer among all monomers used to produce an acrylic polymer wasconfirmed to be roughly the same as the proportion constituted bymonomer units derived from that monomer in the acrylic polymer for eachof the other examples and comparative examples.

«Organic Solvent Addition Step»

The coagulated and dried material obtained in the drying step wasdissolved in xylene and was subsequently treated through heating underreduced pressure using an evaporator to produce a liquid composition(water content: 82 mass ppm; solid content concentration: 7%) as abinder composition.

<Production of Slurry Composition for Solid Electrolyte Layer>

In a glove box under an argon gas atmosphere (water concentration: 0.6mass ppm; oxygen concentration: 1.8 mass ppm), 100 parts of sulfideglass formed of Li₂S and P₂S₅ (Li₂S/P₂S₅=70 mol %/30 mol %;number-average particle diameter: 1.2 μm; D90: 2.1 μm) as a solidelectrolyte and 2 parts (in terms of solid content) of the bindercomposition obtained as described above were mixed, xylene was furtheradded as an organic solvent, and the solid content concentration wasadjusted to 65 mass %. Mixing was subsequently performed by a planetarymixer to produce a slurry composition for a solid electrolyte layer.

<Production of Slurry Composition for Positive Electrode>

After mixing 100 parts of lithium cobalt oxide (average particlediameter: 11.5 μm) as a positive electrode active material, 150 parts ofsulfide glass formed of Li₂S and P₂S₅ (Li₂S/P₂S₅=70 mol %/30 mol %;number-average particle diameter: 0.4 μm) as a solid electrolyte, 13parts of acetylene black as a conductive agent, and 2 parts (in terms ofsolid content) of the binder composition obtained as described above,further adding xylene as an organic solvent, and adjusting the solidcontent concentration to 78%, 60 minutes of mixing was performed by aplanetary mixer. Thereafter, the solid content concentration was furtheradjusted to 74% with xylene and a further 10 minutes of mixing wassubsequently performed to produce a slurry composition for a positiveelectrode.

<Production of Slurry Composition for Negative Electrode>

After mixing 100 parts of graphite (average particle diameter: 20 μm) asa negative electrode active material, 50 parts of sulfide glass formedof Li₂S and P₂S₅ (Li₂S/P₂S₅=70 mol %/30 mol %; number-average particlediameter: 0.4 μm) as a solid electrolyte, and 2 parts (in terms of solidcontent) of the binder composition obtained as described above, furtheradding xylene as an organic solvent, and adjusting the solid contentconcentration to 60%, mixing was performed by a planetary mixer toproduce a slurry composition for a negative electrode.

<Production of all-Solid-State Secondary Battery>

The slurry composition for a positive electrode was applied onto thesurface of a current collector (aluminum foil; thickness: 20 μm) and wasdried (110° C., 20 minutes) to form a positive electrode mixed materiallayer of 50 μm in thickness and thereby obtain a positive electrode. Inaddition, the slurry composition for a negative electrode was appliedonto the surface of a separate current collector (copper foil;thickness: 18 μm) and was dried (110° C., 20 minutes) to form a negativeelectrode mixed material layer of 30 μm in thickness and thereby obtaina negative electrode.

Next, the slurry composition for a solid electrolyte layer was appliedonto the positive electrode mixed material layer surface of the positiveelectrode and was dried (110° C., 10 minutes) to form a solidelectrolyte layer of 18 μm in thickness and thereby obtain a solidelectrolyte layer-equipped positive electrode.

The solid electrolyte layer-equipped positive electrode and the negativeelectrode were affixed with the solid electrolyte layer of the solidelectrolyte layer-equipped positive electrode and the negative electrodemixed material layer of the negative electrode in contact and were thenpressed to obtain an all-solid-state secondary battery. The thickness ofthe solid electrolyte layer in the all-solid-state secondary batteryafter pressing was 11 μm. High-temperature cycle characteristics wereevaluated for this all-solid-state secondary battery. The results areshown in Table 1.

Example 2

A binder composition (water content: 75 mass ppm; solid contentconcentration: 7.5%), various slurry compositions, and anall-solid-state secondary battery were produced, and measurements andevaluations were performed in the same way as in Example 1 with theexception that in production of the binder composition, 2-ethylhexylacrylate was also used as a monomer (proportions among all monomers: 48%ethyl acrylate, 45% n-butyl acrylate, 7% 2-ethylhexyl acrylate) in theemulsion polymerization step, and magnesium sulfate was used instead ofsodium sulfate as a coagulant in the coagulation step. The results areshown in Table 1.

Example 3

A binder composition (water content: 58 mass ppm; solid contentconcentration: 7.5%), various slurry compositions, and anall-solid-state secondary battery were produced, and measurements andevaluations were performed in the same way as in Example 1 with theexception that in production of the binder composition, the number ofwater washes in the washing step was changed to one. The results areshown in Table 1.

Example 4

A binder composition (water content: 88 mass ppm; solid contentconcentration: 7.2%), various slurry compositions, and anall-solid-state secondary battery were produced, and measurements andevaluations were performed in the same way as in Example 1 with theexception that in production of the binder composition, the amounts ofethyl acrylate and n-butyl acrylate used as monomers in the emulsionpolymerization step were changed such that the proportions thereof amongall monomers were 55% and 45%, respectively, 1.3 parts of sodiumdi(polyoxyethylene stearyl ether) phosphate was used instead of 2.5parts of sodium monostearyl phosphate as a phosphoric acid esteremulsifier in the emulsion polymerization step, and the amount of sodiumsulfate used as a coagulant in the coagulation step was changed to 1.2parts. The results are shown in Table 1.

Example 5

A binder composition (water content: 95 mass ppm; solid contentconcentration: 7.8%), various slurry compositions, and anall-solid-state secondary battery were produced, and measurements andevaluations were performed in the same way as in Example 1 with theexception that diisobutyl ketone was used instead of xylene inproduction of the binder composition, the slurry composition for a solidelectrolyte layer, the slurry composition for a positive electrode, andthe slurry composition for a negative electrode. The results are shownin Table 1.

Example 6

A binder composition (water content: 45 mass ppm; solid contentconcentration: 8.2%), various slurry compositions, and anall-solid-state secondary battery were produced, and measurements andevaluations were performed in the same way as in Example 1 with theexception that n-butyl ether was used instead of xylene in production ofthe binder composition, the slurry composition for a solid electrolytelayer, the slurry composition for a positive electrode, and the slurrycomposition for a negative electrode. The results are shown in Table 1.

Comparative Example 1

A binder composition (water content: 68 mass ppm; solid contentconcentration: 7.4%), various slurry compositions, and anall-solid-state secondary battery were produced, and measurements andevaluations were performed in the same way as in Example 1 with theexception that in production of the binder composition, the amount ofsodium monostearyl phosphate used as a phosphoric acid ester emulsifierin the emulsion polymerization step was changed to 7.2 parts. Theresults are shown in Table 2.

Comparative Example 2

A binder composition was produced in the same way as in Example 1 withthe exception that the amount of sodium monostearyl phosphate used as aphosphoric acid ester emulsifier in the emulsion polymerization step inproduction of the binder composition was changed to 0.1 parts, but therecovery rate of an acrylic polymer was extremely low (33%) because theamount of the phosphoric acid ester emulsifier was insufficient andpolymerization stability could not be ensured, and thus various slurrycompositions and an all-solid-state secondary battery were not produced.

Comparative Example 3

A binder composition (water content: 66 mass ppm; solid contentconcentration: 7.2%), various slurry compositions, and anall-solid-state secondary battery were produced, and measurements andevaluations were performed in the same way as in Example 1 with theexception that in production of the binder composition, 1.2 parts ofsodium lauryl sulfate and 3.3 parts of polyoxyethylene dodecyl etherwere used instead of 2.5 parts of sodium monostearyl phosphate as aphosphoric acid ester emulsifier in the emulsion polymerization step.The results are shown in Table 2.

Comparative Example 4

A binder composition (water content: 87 mass ppm; solid contentconcentration: 7%), various slurry compositions, and an all-solid-statesecondary battery were produced, and measurements and evaluations wereperformed in the same way as in Example 1 with the exception that inproduction of the binder composition, the washing step was notperformed, and the hydrous crumbs obtained in the coagulation step weresubjected to the drying step in that form. The results are shown inTable 2.

In Tables 1 and 2, shown below:

“XY” indicates xylene;

“DIK” indicates diisobutyl ketone; and

“BE” indicates n-butyl ether.

TABLE 1 Example Example Example Example Example Example 1 2 3 4 5 6Emulsion Monomers Ethyl acrylate [mass %] 50 48 50 55 50 50 polymer-n-Butyl acrylate [mass %] 50 45 50 45 50 50 ization 2-Ethylhexylacrylate [mass %] — 7 — — — — step Emulsifier Sodium monostearylphosphate 2.5 2.5 2.5 — 2.5 2.5 [parts by mass] Sodiumdi(polyoxyethylene stearyl ether) — — — 1.3 — — phosphate [parts bymass] Sodium lauryl sulfate [parts by mass] — — — — — — Polyoxyethylenedodecyl ether [parts by mass] — — — — — — Initiator Potassium persulfate[parts by mass] 0.22 0.22 0.22 0.22 0.22 0.22 Coagulation CoagulantSodium sulfate 3.3 — 3.3 1.2 3.3 3.3 step [parts by mass (per 100 partsof emulsion polymerization liquid)] Magnesium sulfate — 3.3 — — — —[parts by mass (per 100 parts of emulsion polymerization liquid)]Washing Water [parts by mass (per 100 parts of hydrous crumbs)] 200 200200 200 200 200 step Number of washes [times] 4 4 1 4 4 4 BinderRecovery rate of acrylic polymer [mass %] 100 100 100 94 100 100composition Content of emulsifier [mass ppm] 7700 7500 12500 860 77007700 Content of coagulant [mass ppm] 2500 3100 4500 1100 2500 2500Organic solvent XY XY XY XY DIK BE All-solid- Initial capacity [mAh] 5.55.8 5.5 5.6 5.5 5.5 state High- Capacity maintenance rate (20 cycles)[%] 98 97 88 94 87 85 secondary temperature Capacity maintenance rate(50 cycles) [%] 93 93 83 89 79 78 battery cycle Capacity maintenancerate (100 cycles) [%] 85 88 80 81 75 72 characteristics

TABLE 2 Comparative Comparative Comparative Comparative Example ExampleExample Example 1 2 3 4 Emulsion Monomers Ethyl acrylate [mass %] 50 5050 50 polymer- n-Butyl acrylate [mass %] 50 50 50 50 ization2-Ethylhexyl acrylate [mass %] — — — — step Emulsifier Sodiummonostearyl phosphate 7.2 0.1 — 2.5 [parts by mass] Sodiumdi(poloxyethylene stearyl ether) — — — —- phosphate [parts by mass]Sodium lauryl sulfate [parts by mass] — — 1.2 — Polyoxyethylene dodecylether [parts by mass] — — 3.3 — Initiator Potassium persulfate [parts bymass] 0.22 0.22 0.22 0.22 Coagulation Coagulant Sodium sulfate 3.3 3.33.3 3.3 step [parts by mass (per 100 parts of emulsion polymerizationliquid)] Magnesium sulfate — — — — [parts by mass (per 100 parts ofemulsion polymerization liquid)] Washing Water [parts by mass (per 100parts of hydrous crumbs)] 200 200 200 — step Number of washes [times] 44 4 — Binder Recovery rate of acrylic polymer [mass %] 100 33 100 100composition Content of emulsifier [mass ppm] 33000 420 38000 24000Content of coagulant [mass ppm] 3800 3300 2800 27800 Organic solvent XYXY XY XY All-solid- Initial capacity [mAh] 5.4 — 5.5 5.5 state High-Capacity maintenance rate (20 cycles) [%] 89 — 81 79 secondarytemperature Capacity maintenance rate (50 cycles) [%] 81 — 71 66 batterycycle Capacity maintenance rate (100 cycles) [%] 68 — 60 42characteristics

It can be seen from Table 1 that an all-solid-state secondary batteryhaving excellent high-temperature cycle characteristics was obtained ineach of Examples 1 to 6 in which a solid electrolyte-containing layerwas produced using a binder composition that contained an acrylicpolymer and a phosphoric acid ester emulsifier and had a phosphoric acidester emulsifier content within a specific range.

On the other hand, it can be seen from Table 2 that high-temperaturecycle characteristics (particularly the capacity maintenance rate after50 cycles and 100 cycles) of an all-solid-state secondary battery werelost in each of Comparative Examples 1 and 4 in which a solidelectrolyte-containing layer was produced using a binder compositionhaving a phosphoric acid ester emulsifier content that exceeded aspecific upper limit.

It can also be seen from Table 2 that the recovery rate of an acrylicpolymer significantly decreased as previously described in ComparativeExample 2 in which the content of a phosphoric acid ester emulsifier ina binder composition was lower than a specific lower limit as a resultof the amount of the phosphoric acid ester emulsifier used in productionof the binder composition being reduced.

It can also be seen from Table 2 that high-temperature cyclecharacteristics of an all-solid-state secondary battery were lost inComparative Example 3 in which an emulsifier other than a phosphoricacid ester emulsifier was used in production of a binder composition.

INDUSTRIAL APPLICABILITY

According to the present disclosure, it is possible to provide a bindercomposition for an all-solid-state secondary battery and a slurrycomposition for an all-solid-state secondary battery with which it ispossible to form a solid electrolyte-containing layer that can cause anall-solid-state secondary battery to display excellent high-temperaturecycle characteristics.

Moreover, according to the present disclosure, it is possible to providea solid electrolyte-containing layer that can cause an all-solid-statesecondary battery to display excellent high-temperature cyclecharacteristics and an all-solid-state secondary battery that hasexcellent high-temperature cycle characteristics.

1. A binder composition for an all-solid-state secondary batterycomprising: an acrylic polymer; and not less than 500 mass ppm and notmore than 20,000 mass ppm of a phosphoric acid ester emulsifier relativeto the acrylic polymer.
 2. The binder composition for an all-solid-statesecondary battery according to claim 1, wherein the acrylic polymerincludes both an ethyl acrylate unit and an n-butyl acrylate unit. 3.The binder composition for an all-solid-state secondary batteryaccording to claim 1, wherein the acrylic polymer is an emulsionpolymer.
 4. The binder composition for an all-solid-state secondarybattery according to claim 1, further comprising an organic solvent. 5.A slurry composition for an all-solid-state secondary batterycomprising: a solid electrolyte; and the binder composition for anall-solid-state secondary battery according to claim
 4. 6. The slurrycomposition for an all-solid-state secondary battery according to claim5, wherein the solid electrolyte is an inorganic solid electrolyte. 7.The slurry composition for an all-solid-state secondary batteryaccording to claim 5, further comprising an electrode active material.8. A solid electrolyte-containing layer formed using the slurrycomposition for an all-solid-state secondary battery according to claim5.
 9. An all-solid-state secondary battery comprising the solidelectrolyte-containing layer according to claim 8.